This invention relates to a movable contactor device in a circuit breaker such as a wiring breaker or earth leakage breaker.
Heretofore, in a circuit breaker of this type, a switching movable contactor is, in general, electrically connected through a flexible conductor to a connecting conductor secured to the body casing of the circuit breaker. The flexible conductor is repeatedly bent as the movable contactor operates, and therefore it may be fatigued and broken. Further, a resistance force applied to the movable contactor by the flexible conductor is variable, thus changing the switching characteristic of the circuit breaker. Those difficulties are noticeable especially with a circuit breaker of middle or more size having a flexible conductor large in diameter.
In order to eliminate those difficulties, a movable contactor device which does not have the flexible conductor has been disclosed by Japanese Patent Application (OPI) No. 19938/1992. In the device, a pair of arms are provided at the end portion of the connecting conductor on the stationary side which is connected to the movable contactor, in such a manner that they hold the movable contactor therebetween. The arms are pushed against the side surfaces of the movable contactor with springs, so that the movable contactor is slidably and electrically connected to the connecting conductor. That is, the disclosed device is dispensed with the above-described flexible conductor.
When, with the circuit breaker closed, the movable contact and the stationary contact are completely in parallel with each other horizontally (or in the direction of width), the contact surface of the movable contact which is generally arcuate in a front-to-rear direction is brought in linear contact with the contact surface of the stationary contact which is flat as a whole.
However, because of the assembling error, and depending on the accuracies of the components of the circuit breaker, it is difficult to maintain the movable contact and the stationary contact completely in parallel with each other; that is, those contacts are somewhat inclined in the direction of width. In the above-described slide contact type movable contactor device, the movable contact is greatly restricted with respect to free inclination constructionally because the slide contact portion of the movable contact is pinched by the connecting conductor. That is to say, even though, with the circuit breaker closed, the movable contact is greatly pushed against the stationary contact, the play is less which permits the movable contact to change its posture so as to be sufficiently in contact with the stationary contact. Consequently, a so-called "non-uniform contact" phenomenon occurs; that is, the movable contact is brought into contact with the stationary contact on only one side, right side or left side.
In the case of a small circuit breaker of small rated current, the adverse effects of this non-uniform contact on it are not so serious; however, in the case of a middle or large circuit breaker, the contact resistance generates heat, thus increasing the terminal temperature. With a large circuit breaker whose rated current is for instance 600 A or higher, the current handled thereby is large, and therefore the thickness of the movable contactor and the width of the movable contact welded thereto are more than 10 mm. Accordingly, in the large circuit breaker, it is more difficult to maintain the degree of parallelization of the movable contact and the stationary contract than in a small circuit breaker, and the problem that heat is generated because of the above-described non-uniform contact is more serious.
In view of the foregoing, an object of this invention is to provide a movable contactor device of slide contact type in which the contact area of the movable contact and the stationary contact is increased, and which is applicable particularly to a large circuit breaker.
Beside, the interrupting capacity of a circuit breaker depends on how the stress is reduced which is attributed to the arc energy produced when the current is cut off. Means for reducing the stress is, typically, a current limiting mechanism. The current limiting mechanism operates as follows: When short-circuit current flows in the circuit breaker, the current limiting mechanism quickly moves the movable contactor to open the contact means before the contact opening operation is achieved by the tripping operation of the switching mechanism, so that the arc voltage is increased, and the current limiting interruption is quickly achieved.
The current limiting mechanism performs an unlatching operation by using an electromagnetic repulsion force which is induced by the current which flows in the opposite directions in two conductors arranged in parallel with each other. The above-described current limiting interruption is advantageous in that, at the interruption of short-circuit current, the current peak value and the let-through I.sup.2 t value are suppressed, and thermal and mechanical stresses applied to the path of current are greatly reduced.
The key point of the current limiting interruption resides in that the speed of movement of the movable contactor to open the contact means is increased maximum, so that the arc produced in sticking state is quickly made active, to improve the current limiting effect.
On the other hand, in the case where a large circuit breaker is employed to handle large current, the movable contactor is accordingly large in weight, and, when the contact means is opened, the inertial moment of the movable contactor is increased as much, which makes it difficult to increase the speed of movement of the movable contactor to open the contact means.
In view of the foregoing, an object of this invention is to provide a movable contactor device for a circuit breaker in which, at the time of current limiting interruption, the movable contactor is moved at high speed to open the contact means, and which is applicable to a large circuit breaker in which heretofore the in current limiting effect is not so great.